Found it.

https://electionlawblog.org/?p=146397

52 U.S.C. 10307©: “Whoever knowingly or willfully gives false information as to his name, address or period of residence in the voting district for the purpose of establishing his eligibility to register or vote, or conspires with another individual for the purpose of encouraging his false registration to vote or illegal voting, or pays or offers to pay or accepts payment either for registration to vote or for voting shall be fined not more than $10,000 or imprisoned not more than five years, or both…”

DOJ Election Crimes Manual at 44: “The bribe may be anything having monetary value, including cash, liquor, lottery chances, and welfare benefits such as food stamps. Garcia, 719 F.2d at 102. However, offering free rides to the polls or providing employees paid leave while they vote are not prohibited. United States v. Lewin, 467 F.2d 1132, 1136 (7th Cir. 1972). Such things are given to make it easier for people to vote, not to induce them to do so. This distinction is important. For an offer or a payment to violate Section 10307©, it must have been intended to induce or reward the voter for engaging in one or more acts necessary to cast a ballot.… Moreover, payments made for some purpose other than to induce or reward voting activity, such as remuneration for campaign work, do not violate this statute. See United States v. Canales 744 F.2d 413, 423 (5th Cir. 1984) (upholding conviction because jury justified in inferring that payments were for voting, not campaign work). Similarly, Section 10307© does not apply to payments made to signature-gatherers for voter registrations such individuals may obtain. However, such payments become actionable under Section 10307© if they are shared with the person being registered.”